The present invention relates to a magnetic brush forming device for use an image generating apparatus for generating a visible image by developing an electrostatic latent image with toner.
There have been known image generating apparatus for developing an electrostatic latent image on a latent image carrier into a visible image with toner in a developing device, transferring the visible image onto a transfer member, and cleaning remaining toner from the latent image carrier with a cleaning device. Such an image generating apparatus may be employed in an electrophotographic copying machine, a printer, a facsimile transmitter/receiver, or the like. It is also widely known to employ a magnetic brush forming device as the developing device or the cleaning device of the type described above, and these devices are generally referred to respectively as a magnetic brush developing device and a magnetic brush cleaning device. In the magnetic brush developing device, a brush carrier carries a developing agent for developing a latent image into a visible image. In the magnetic brush cleaning device, a brush carrier carries a cleaning agent for cleaning toner away from the latent image carrier.
The agent, which may be a developing agent or a cleaning agent, is carried as a layer on the brush carrier in the magnetic brush forming apparatus, and the thickness of the layer is limited or controlled by a limiting member. When the layer thickness is limited by the limiting member, the layer of the agent is squeezed by the limiting member, producing heat due to physical contact between the layer and the limiting member. Therefore, the temperature of the agent is increased to cause toner to be fused with time to the surface of carrier particles in the agent. When such fusion of the toner takes place, the ability of the magnetic brush cleaning device to clean remaining toner from the latent image carrier is lowered, and the latent image carrier in the magnetic brush developing apparatus tends to bring about undesirable toner deposits or "scumming" thereon.
The magnetic brush developing device and the magnetic brush cleaning device each employ a magnet roll comprising a sleeve with its outer circumferential portion made of a nonmagnetic material and a magnet loosely fitted in the sleeve.
The magnet roll is operated in one of the following modes: (1) The sleeve is rotated and the magnet is fixed. (2) The magnet is rotated and the sleeve is fixed. (3) Both the sleeve and the magnet are rotated. In each of these operating modes, the sleeve and the magnet produce relative movement therebetween, i.e., they are relatively rotated or moved.
Utilizing the relative rotation of the sleeve and the magnet, a magnetic brush is caused to roll on the outer circumferential surface of the sleeve to either supply toner to a photosensitive body in the magnetic brush developing device or remove remaining toner from a photosensitive body in the magnetic brush cleaning device.
In order to achieve the relative rotation of the sleeve and the magnet, the sleeve or the magnet or both are rotatably supported in various supporting arrangements. Two conventional arrangements for supporting the sleeve and the magnet to allow their relative rotation will be described below.
According to one system, the outer circumferential portion of the sleeve at its opposite ends is rotatably supported on side plates, and a gear is fixed to an extension of the outer circumferential portion of the sleeve at one end for transmitting rotary motion to the sleeve. A magnet support shaft is rotatably supported centrally on flanges on the opposite ends of the sleeve, and has one end extending outwardly from the flange and fixed to a stationary member.
According to another structure, the outer circumferential portion of the sleeve at one end thereof is rotatably supported on a side plate, and a gear is fixed to an extension of the supported outer circumferential portion of the sleeve for transmitting rotary motion to the sleeve. A magnet support shaft is rotatably supported centrally on flanges on the opposite ends of the sleeve. The magnet support shaft extends outwardly from the flange at the other end of the sleeve and is fixed to a side plate to support the other end of the sleeve.
In each of the above support arrangements, the magnet is fixedly mounted on the magnet support shaft, and the sleeve is rotatable with respect to the fixed magnet. The flanges on the opposite ends of the sleeve serve to virtually close the inner space of the sleeve.
The magnet roll generally produces heat due to (1) friction between the sleeve and the developing agent (carrier and toner), (2) an eddy current produced upon relative movement of the sleeve (made of metal) and the magnet, and (3) heat transfer from another unit such as a fixing heater.
When the magnet roll is heated, it thermally fuses the developing agent which contains a synthetic resin component. Such thermal fusion should be avoided as it would largely impair the developing o cleaning capability of the magnetic roll.
However, with the aforesaid conventional support schemes, the inner space of the sleeve is fully closed and tends to store heat therein. Since the heat stored in the sleeve cannot easily be dissipated, it is responsible for lessening the developing or cleaning capability.